1. Field of the Invention
The present invention relates to a mold for resin sealing (hereinafter referred to as "resin sealing mold") and more particularly to a resin sealing mold which can smoothly release a package and prevent resin from remaining.
2. Description of the Related Art
A package for constituting the appearance of a semiconductor device has conventionally manufactured in the following manner.
First, a resin sealing mold having a cavity is arranged on a resin sealing region of a lead frame. Thereafter, the cavity is filled with resin, and the filled resin is hardened by heating to form a package.
The surface of the cavity of such a resin sealing mold is satin-finished so that the package can be smoothly released from the cavity. The satin-finished surface can be formed by discharging processing and sandblasting for the cavity surface. The cavity having a satin-finished surface is disclosed in e.g. JP-A-6-143360.
However, in recent years, a package having a structure in which an external leads is exposed from a bottom of the sealing resin, such as "SON" (Small Outline Non-leaded) or "QFN" (Quad Flat Non-leaded) has been developed for commercial use. In such as structure, a bottom surface of the leads is exposed from the bottom surface of the package so that the bottom surface of the leads can be contacted to a wiring layer of an outer circuit such as printed circuit board. Therefore these structure has an advantage that mounting area can be reduced. However, where the package having a SON structure or QFN structure is made by resin sealing using the mold with the cavity surface satin-finished, resin remains on the exposed external leads which may lead to connection failure in packaging.
FIG. 7 is a sectional view of a conventional mold structure which shows the manner of deposition of resin on an external lead. As seen from the figure, in the case of using the conventional mold, the external lead 18 is placed on a satin-finished region 24, and a minute space M is formed between the external lead 18 and a mold 100. When resin sealing is executed in such a state, the sealing resin injected into the cavity 14 invades the above minute space M, i.e. areas indicated by arrow in FIG. 2 so that the resin is deposited on the surface of the external lead 18. Thereafter, when the mold 100 is hardened by heating, the resin deposited on the external lead 18 is also hardened as it is so that it remains on the external lead 18 after the package is released from the mold . This remaining resin may leads to connection failure in packaging.
On the other hand, the satin-finished region formed on the surface of a cavity 14 is an important component for smoothly releasing a package so that such a region as wide as possible are preferably formed. Accordingly, it is necessary to prevent the resin from being deposited on the external lead while the satin-finished region is left.
Thus, in a semiconductor device such as the SON structure or QFN having a structure in which external leads are exposed from a bottom of the sealing resin, the portion of the leads embedded into the sealing resin is relatively short so that it is difficult to assure sufficient contact between the external leads and the resin. Therefore, great force applied to the external leads when the package is released may give rise to falling out of the lead. The resin deposited on the rear face of the external leads may lead to connection failure of the package.